1. Field of the Invention
The present invention relates to an inference system used in a reactor power plant, a trouble diagnosing system, and so forth.
2. Description of the Related Art
Recently, an inference system using Rete algorithm has been well known as a means for accomplishing an AI machine.
The inference system uses a production rule composed of an "if statement" and a "then statement" to execute an inferential operation.
First, the "if statement" of each of the production rules and of those permitted by another rule or the like is successively compared with current fact information in a working memory. Thus, a plurality of production rules which satisfy each "if statement" are retrieved as candidates. Thereafter, the most suitable one of the production rules being retrieved is selected. Thereafter, the "then statement" of the selected production rule is executed.
The cost of time, memory storage, and so forth used for the comparison of the rules in the inferential operation depends on the contents of the production rules and the working memory.
For example, assume the following two production rules.
Rule 1.
if (c&gt;1)
then A :=c+1.5
Rule 2.
if (c&gt;1) and (f (c)&gt;c)
then A :=c+1.25
where f(c) of the rule 2 is a function where the computing time varies depending on the state of "c". Thus, the time required for comparison of the rule 2 depends on the state of "c". In a particular state of "c", the time required for comparison of the rule 2 becomes longer than that for the rule 1.
Thus, when an inference system is used in a process system which should retrieve a subsequent operational candidate with a limited resource (time and memory capacity), a large risk would result.
For example, for controlling a reactor power plant or the like, a particular process should be executed within a particular time after a trouble takes place. However, in the aforementioned inference system, it is not assured that an operational candidate is always selected in the limited time. If an operational candidate is not selected in the limited time, in the worst case, the process operation stops and thereby a critical trouble may take place.